Solar collector panels for heating of water for domestic use or for space heating are well known in the art, but also solar collector panels for heating of air, either to be used directly for ventilation and space heating or as a medium for conveying heat to a heat exchanger is known.
The French patent application FR 2500036 shows a typical, simple solar collector panel comprising a transparent front panel, a heat absorbing back panel which is thermally insulated at the back wall, and a passage between the front panel and the back panel, which has an inlet opening at the bottom for allowing cold air to flow into the passage and an outlet opening at the top for exit of the air heated by passing the back panel. The back wall of the back panel facing away from the front panel is thermally insulated to prevent a heat flow from the heat absorbing back panel and out of the solar collector panel.
U.S. Pat. No. 4,054,124 discloses a more sophisticated solar collector panel, in which a perforated heat absorber panel is inserted between the transparent front panel and the thermally insulated back panel. The inlet air flows from the side of the solar collector panel into the space between the front panel and the heat absorber panel, through the perforations at which the air is heated and out from the space between the heat collector panel and the thermally insulated back panel. A much higher heat transfer coefficient between the air and the heat absorber is obtained thereby as compared to the disclosure of FR 2500036.
In U.S. Pat. No. 4,262,657 more variants of solar collector panels are disclosed, using the feature of a permeable heat absorber panel through which the air flows to be heated. It is a common feature of the variants that the back wall of the solar collector panels is thermally insulated to improve the thermal efficiency of the solar panel.
The combination of a solar collector panel for heating of air and a photovoltaic cell panel arranged behind the transparent front panel and in front of the heat collector panel is disclosed in GB 2 214 710. The heat collector plate is thermally insulated towards the exterior and a transparent panel between the photovoltaic cell panel and the heat collector panel separates airflows parallel to the panels to cool the photovoltaic cell panel and to extract heat from the heat collector panel, respectively.